The present invention relates generally to controlling an electromagnetic valve actuator, and more particularly to control methods for electromagnetic engine valve actuation with variable timing to improve combustion control and fuel economy for an internal combustion engine.
Typically in an internal combustion engine, the intake and exhaust valves are controlled mechanically. The valves are tied to the engine""s crankshaft and thus there is limited flexibility in the control of the valves. Valve control is extremely important for optimizing fuel economy and reducing polluting emissions. Therefore, flexibility is highly desirable in valve control.
It is known in the art to employ electromagnetically driven valve actuators in an internal combustion engine. Typically, these known systems require power circuits having high frequency switching devices in order to handle the voltage differences required to properly control the valves. Additionally, the control of the valve timing is critical and therefore, is the subject of much consideration.
Improving the timing of the electromagnetically driven valves not only improves the engine""s combustion capabilities, but may also reduce the pumping losses for air charging, thereby improving fuel economy and reducing emissions. Determination of the optimum current that should be applied to the opening and/or closing coils, and reducing the amount of excitation current that is required, are ongoing subjects of research.
It is an object of the present invention to control the electromagnetic engine valve actuation system using current-commanded control. It is another object of the present invention to use back electromotive force (emf) to compensate for nonlinear feedback control.
It is a further object of the present invention to provide an initialization sequence for the above mentioned control techniques that reduces the amount of initialization current required by an actuator.
In carrying out the above objects and other objects and features of the present invention, a method is provided that improves the timing of an electromagnetic valve actuator by improving the valve control. In one embodiment of the present invention, a desired current is calculated based on feedback from the actuator and a power circuit generates the desired current in order to produce the force necessary to operate the actuator. In another embodiment of the present invention the current control method is enhanced by applying estimated back emf in order to calculate a desired voltage. The desired voltage is used to generate the voltage necessary to obtain the desired current, which will ultimately control the actuator. The back emf method of the present invention eliminates the need for any current regulation in the power stage, thereby reducing the size, complexity and ultimately the cost of the power stage.
Additionally an initialization method is provided which reduces the amount of current required to initialize a coil of the actuator. According to the initialization method of the present invention, a sequence of pulses is applied to the closing coil at predetermined intervals in order to enhance the natural frequency of oscillations and thereby generate a sufficient initialization pulse without the need for excessive current. Smaller current requirements will allow a reduction in the size of the closing coil to be realized, thereby increasing packaging space for other applications and at the same time reduce the weight and cost of the electromagnetic valve system.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.